This invention relates to electronic communication; and more particularly, it relates to methods and apparatus for simultaneously transmitting isochronous and nonisochronous data on a local area network.
A local area network includes a plurality of stations each of which has an input port and an output port. These stations are intercoupled as one or more loops in which the output part of each station couples to the input port of the next station. If more than one loop exists in the network, then the loops are intercoupled in pairs by one or more bridge stations.
Isochronous data is data which is transmitted in parts by a station on the network at fixed periodic intervals. A station which every 125 microseconds, transmits one byte of data in 0.16 microseconds, is transmitting isochronously. Such a transmission occurs, for example, when voice samples of a telephone conversation are being transmitted.
Nonisochronous data is data which is transmitted all at once in a block. For example, a station that transmits 70 bytes of data one time as a contiguous block of bytes is transmitting nonisochronously. Such a transmission occurs, for example, when a record or file is being sent from one station to another.
One important parameter of a local area network is the amount of time that it takes for data to pass from the input port of a station to the output port. Preferably, this delay is short because certain types of isochronous data (e.g., telephone voice samples) must make the round trip through all the stations of a local area network loop within an upper time limit. Thus, as the per station delay gets shorter, the total number of stations on the loop can increase.
Another important parameter of a local area network is the amount of circuitry that each station is required to have in order to transmit isochronous and nonisochronous data in the network. Preferably, this circuitry is minimal so the cost of adding a station is low.
Both the delay through a station and amount of circuitry that a station is required to have to transmit on the network are dependent upon the method by which data is sent on the network. Accordingly, a primary object of the invention is to provide an improved method of simultaneously transmitting isochronous and nonisochronous data on a local area network which reduces delay through and circuitry in stations on the network.